Heavy duty switch held in closed position by parallel current branches and assisted in movement to open position by antiparallel branches



March 1, 1966 H. FEHLING 3,238,339

HEAVY DUTY SWITCH HELD IN CLOSED POSITION BY PARAL CURRENT BRANCHE S ANDASSISTED IN MOVEMENT TO OPEN PO TION BY ANTIPARALLE L BRANCHES FiledMarch 12, 1962 I Hm: Icwn Qttovnag Jnvenfor:

United States Patent O 3,238,339 HEAVY DUTY SWITCH HELD IN CLOSED POSI-TION BY PARALLEL CURRENT BRANCHES AND ASSISTED IN MOVEMENT TO OPEN P051-TION BY ANTIPARALLEL BRANCHES Heinz Fehling, Mecklenburger Weg, Einfeld,near Neumunster, Germany, assignor to LicentiaPatent-VerwaItungs-G.m.b.H., Frankfurt am Main, Germany Filed Mar. 12,1962, Ser. No. 179,052 Claims priority, application Germany, Mar. 13,1961, L 38,422 7 Claims. (Cl. 200-146) tThe present invention relates tothe electric switching ar More particularly, the present inventionrelates to a heavy duty switch which is capable of handling largeamounts of currents and which will open when the current reaches a givenrated current, i.e., a heavy duty circuit breaker havingcurrent-limiting characteristics. Switches of this type require contactelements in which the current communication from the main contactportion to the contact portion at which the arc is ignited occurssatisfactorily, even when the current is interrupted at high speed. Itis particularly important that the main contact portions will mot bedamaged during switch opening. Such damage can be caused as the resultof short-circuit current pulses having a high peak value, or as theresult of the electrodynamic forces within the portions of high currentdensity of the points of engagement of the contact elements, or as theresult of current loops formed by the current leads connected to thecontact elements.

Recently, current-limiting circuit breakers have been developed in whichelectrodynamic and magnetic forces produced by the short-circuit currentare used for opening the contact system. If such circuit breakers areused as overload switches for protecting a motor which is difficult tostart, then the switch should not open until the short-circuit currentis more than eight to sixteen times the rated current of the switch;until such current value has been reached, the switch must remaininsensitive to the electrodynamic forces.

It is, therefore, an object of the present invention to provide a switchwhich is able to fulfill the above requirements, and, with this objectin view, the present invention resides mainly in a switch whichcomprises movable and stationary contact members provided with contactsthat serve to conduct current when the switch is closed, as well as witharching contacts which carry the current just prior to the time theswitch assumes its open position. According to the instant invention,the arrangement of the contacts is such that, so long as the switch isclosed, the current through the two contact members will flow inparallel current branches, thereby creating electrodynamic forcestending to maintain the switch in closed position, whereas when theswitch has moved from its closed position to an intermediate position,the current through the two contact members will flow in antiparallelcurrent branches which create electrodynamic forces tending to urge theswitch into the open position. More particularly, each contact memberhas sequentially arranged and spaced-apart main, intermediate and arcingcontacts which cooperate with respective sequentially arranged andspaced-apart main, intermediate and arcing contacts of the other contactmember. In closed position, the main and intermediate arcing contactsare in engagement with each other, and, as the switch moves into itsintermediate position, the intermediate and arcing contacts will atfirst be in engagement with each other whereafter only the arcingcontacts will be in engagement with each other. To assist this move-3,238,339 Patented Mar. 1, 1966 ment, one of the intermediate contactsis fashioned as a roll-off type contact about which the movable contactmember moves, the entire arrangement being, as stated above, such thatthe current flows in parallel branches while the switch is closed,thereby helping to maintain the switch closed, but in antiparallelbranches as the switch is in the process of being opened, therebyhelping the opening.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawings in which:

FIGURE 1 is an elevational view of one embodiment of a switch accordingto the present invention.

FIGURE 1a is a schematic diagram showing the current flow through theswitch illustrated in FIGURE 1.

FIGURE 2 is a perspective view of the stationary contact member of theswitch of FIGURE 1.

FIGURE 3 is a sectional elevation of a modified embodiment of a switchaccording to the present invention.

FIGURE 3a is a schematic diagram showing the current flow through theswitch illustrated in FIGURE 2.

Referring now to the drawings, FIGURES 1 and 2 show a contactarrangement according to the instant invention which comprises astationary contact member 1 and a movable contact member 2. The member 1carries sequentially arranged and spaced-apart first, second and thirdcontacts 3a, 4a, and 5a, which cooperate with respective sequentiallyarranged and spaced-apart first, second and third contacts 3b, 4b, 5b,carried by member 2. In practice, contacts 3b and 4b may simply bedifferent portions of a single contact bridge affixed to the contactmember 2. The main contacts 3a, 3b, and the intermediate contacts 4a,4b, constitute main contact means whereas the contacts 5a, 5b, arearcing contacts. The current lead 6 is in the form of a bus barconnected to the contact member 1 at a point closest to the contact 4a,whereas the lead 7, which is flexible so as to allow the contact member2 to be moved relative to the sta tionary contact member 1, is closestto the contact 3b.

The contact member 2 is movable relative to the stationary contactmember 1 from the closed position shown in FIGURE 1, wherein the mainand intermediate contacts 3a, 3b; 4a, 4b, are in engagement with eachother, through an intermediate position in which at first theintermediate contacts 4a, 4b, and the arcing contacts 5a, 5b, are inengagement with each other but after which only the arcing contacts 5a,5b, are in engagement with each other, to an open position in which noneof the contacts is in engagement with any other and in which thespring-biased roller element 8 will slide off the cam surface 9. Inorder to allow this type of movement, the contact 4:: is fashioned as aroll-off contact.

The current flow through the contact members is depicted in FIGURE 10.Since the main and intermediate contacts 3a, 3b; 4a, 4b, are closed andthe arcing contacts 5a, 5b, are open, the current coming in via lead 6and leaving via lead 7 is divided into two parallel current branches orpaths. These branches create forces which tend to maintain the movablecontact member 2 in its closed position. If the contact arrangementprovides for a three-point engagement, as shown in FIGURE 3, the force Pwhich tends to separate the contacts may be obtained by the following,empirically derived equation:

where n=the number of contact points. On the other hand, the force Kwhich tends to urge toward each other two parallel conductors of finitelength through which current flows is represented by the followingequation:

where L is the length of the two conductors and a the average distancebetween the conductors. In order to obtain a force which tends toincrease contact pressure, K must be larger than P. The equations showthat L/a has to equal C 1.5. If there are 11:3 contact points, it issufficient if the factor C is 1.5 C5, i.e., if the ratio L/a is about 7.According to the present invention, the ratio L/a is so matched to theactuator associated with the switch, i.e., to the current value at whichsuch actuator is actuated, that the switch will remain safely closeduntil the actuator is energized.

Upon actuation by the electromagnetic actuator, both it and theelectrodynamic forces will turn the movable contact about roll-offcontact 4a so that contacts 3a, 3b, .are opened and the arcing contactsa, 5b, enter into engagement. As a result, no more current can flowthrough the parallel current branches. Moreover, as soon as the contacts4a, 4b, are separated, the entire current will 'fiow through the currentloop via contacts 5a, 5b. The current in the two branches will now beantiparallel, i.e., parallel but in the opposite direction. Theelectrodynamic forces are now such that they will assist the movement ofthe movable contact member 2 from its intermediate position to its openposition. The fact that the direction of the cur-rent in the twobranches has now been changed will also bring about a self-generatedstrong magnetic blow-out of the are which will occur at the contacts 5a,5b.

In practice, the current may be fed to the arcing contacts 5a, 5b,either by the bus bar shown in solid lines (FIGURES 1 and 2), or byleads or straps 11, shown in dot-dash lines (FIGURE 1).

The embodiment shown structurally in FIGURE 3 and schematically inFIGURE 3a is similar to the abovedescribed one in that it also includesstationary and movable contact members 1' and 2' carrying contacts 3a,3b, 4a, 4b, 5a, and 5b, as well as leads 6 and 7, and the spring-biasedroller element 8' and cam 9'. However, the stationary contact member,instead of being a single piece, comprises a first part to which thecontacts 3a and 4a are afiixed and a second part 13 which is pivotallymounted on a pin 12. The part 13, whose rightwardly-directed bulge, asviewed in FIGURE 3, constitutes the arcing contact 5a, is yieldable andis acted upon by a spring 13a carried by a rod 1311 which itself ispivotally connected to the part 13 and passes through a stationary stud15. A strap 14 is provided for establishing a satisfactory elec tricalconnection between the part 13 and the lead 6'. The arrangement of thepants is thus such that, when the movable contact member is in itsclosed position, all of the cooperating contacts, including the arcingcontacts 5a, 5b, are in engagement with each other so that the currentthrough the switch is divided into three pants, there being, as bestshown in FIGURE 3a, a parallel current branch as well as an antiparallelcurrent branch.

By properly selecting the contact pressure as well as the correct ratioof the length of the parallel branch to the length of the antiparallelbranch, the force which tends to urge the contacts 301, 3b; 4a, 4b,together will not be reduced. Only when the electrodynamic or magnetictripping actuator is energized will the movable contact member 2 rolloff contact 4a and press the part 13 rearvvardly until it abuts the headof the stud 15, the parts then assuming the position shown in dashedlines. The movable contact member is then in its intermediate positionand the entire current will flow through the arcing contacts.Consequently, the current wiil flow only in antiparatllel branches andthe electrodylnamic forces will urge the contact member 2 toward itsopen position.

The electromagnetic actuator, Le. a tripping device that is actuated bythe current passing the switch, and a trip lever mechanism between themovable contact member and a spring loaded during the switch-in movingof movlable contact member in the switch-in position or looses itaccording to tripping of the actuator for travelling in the switch-outposition may be of conventional form.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes, andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

What is claimed is:

1. A switch comprising an elongated stationary contact member and anelongated movable contact member, each contact member having a meanswhich forms an elongated current conductive path, the two currentconductive paths, throughout substantially their entire lengths, beinggenerally parallel to each other and in close proximity to each inconsequence of which the two magnetic fields which result firom the flowof current through the respective current conductive paths will affecteach other, each contact member carrying, along the lengths of itsrespective means which forms the elongated current conductive path,sequentially arranged and spaced-apart main, intermediate and arcingcontacts which cooperate with respective sequentially arranged andspaced-apart main, intermediate and arcing contacts of the other contactmember, a current lead connected to one of said contact members at apoint thereon closest to its main contact and another current leadconnected to the other of said contact members at a point thereonclosest to its intermediate contact, said movable contact member beingmovable relative to said stationary contact member from a closedposition in which at least said main and intermediate contacts are inengagement with each other, thereby causing ciongatted parallel currentbranches in said conductive paths of said stationary and movable contactmembers which tend to maintain said movable contact member in its closedposition, to an intermediate position in which only said arcing contactsare in engagement with each other, thereby causing elongatedantiparallel current branches in said conductive paths of saidstationary and movable contact members which tend to move said movablecontact member out of its intermediate position toward its open positionin which none of said contacts is in engagement with any other.

2. A switch as defined in claim 1, wherein the intermediate contact ofone of said contact members is a rolloff type contact about which saidmovable contact member moves fromits closed position to its intermediateposition.

3. A switch as defined in claim 1, wherein said arcing contacts are outof engagement with each other when said movable contact member is in itsclosed position, whereby when said movable contact member is in itsclosed position there will be only parallel current branches in saidcontact members.

4. A switch as defined in claim -1, wherein said arcing contacts arealso in engagement with each other when said movable contact member isin its closed position, whereby when said movable contact member is inits closed position, there will be both parallel and antiparalllelcurrent branches in said contact members.

5. A switch as defined in claim 4, wherein said static ary contactmember comprises a first part carrying said stationary main andintermediary contacts and a second part which is yieldably mounted onsaid first part and carries the arcing contact pertaining to saidstationary contact member.

6. A switch as defined in claim 1, wherein said main contact of one ofsaid contact members includes at least one contact element forming abridging contact.

7. A switch comprising an elongated stationary contact member and anelongated movable contact member, each contact member having a meanswhich forms an elongated current conductive path, the two currentconductive paths, throughout substantially their entire lengths, beinggenerally parallel to each other and in close proximity to each inconsequence of which the two magnetic fields which result from the flowof current through the respective current conductive paths will afiecteach other, each contact member carrying, along the length of itsrespective means which forms the elongated current conductive path,sequentially arranged and spaced-apant first, second and third contactswhich cooperate with respective sequentially arranged and spaced-apartfirst, second and third contacts of the other contact member, said firstand second contacts of each contact member constituting a main contactmeans and said third contact constituting an arcing contact, a currentlead connected to one of said contact members at a point thereon closestto its first contact and another current lead connected to the other ofsaid contact members at a point thereon closest to its second contact,said movable contact member being mov able relative to said stationarycontact member from a closed position in which at least said first andsecond contacts of said contact members are engagement with each other,thereby causing elongated parallel current branches said conductivepaths of said stationary and movable contact members which createelectrodyna-mic forces tending to maintain said movable contact memberin its closed position, to an intermediate position in which at firstsaid second and third contacts of said contact members are in engagementwith each other but after which only said third contacts are inengagement with each other, thereby causing elongated antiparallelcurrent branches in said conductive paths of said stationary and movablecontact members which create electrodynamic forces tending to move saidmovable contact member out of its intermediate position toward its openposition in which none of said contacts is in engagement with any other.

References Cited by the Examiner UNITED STATES PATENTS 2,127,813 8/1938Graves 200-87 2,849,579 8/1958 Frink 200146 2,959,654 11/1960 CasWell200-146 KATHLEEN H. CLAFFY, Primary Examiner.

ROBERT K. SCHAEFER, BERNARD A. GILHEANY,

Examiners.

1. A SWITCH COMPRISING AN ELONGATED STATIONARY CONTACT MEMBER AND ANELONGATED MOVABLE CONTACT MEMBER, EACH CONTACT MEMBER HAVING A MEANSWHICH FORMS AN ELONGATED CURRENT CONDUCTIVE PATH, THE TWO CURRENTCONDUCTIVE PATHS, THROUGHOUT SUBSTANTIALLY THEIR ENTIRE LENGTHS, BEINGGENERALLY PARALLEL TO EACH OTHER AND IN CLOSE PROXIMITY TO EACH INCONSEQUENCE OF WHICH THE TWO MAGNETIC FIELDS WHICH RESULT FROM THE FLOWOF CURRENT THROUGH THE RESPECTIVE CURRENT CONDUCTIVE PATHS WILL AFFECTEACH OTHER, EACH CONTACT MEMBER CARRYING, ALONG THE LENGTH OF ITSRESPECTIVE MEANS WHICH FORMS THE ELONGATED CURRENT CONDUCTIVE PATHS,SEQUENTIALLY ARRANGED AND SPACED-APART MAIN, INTERMEDIATE AND ARCINGCONTACTS WHICH COOPERATE WITH RESPECTIVE SEQUENTIALLY ARRANGED ANDSPACED-APART MAIN, INTERMEDIATE AND ARCING CONTACTS OF THE OTHER CONTACTMEMBER, A CURRENT LEAD CONNECTED TO ONE OF SAID CONTACT MEMBERS AT APOINT THEREON CLOSEST TO ITS MAIN CONTACT AND ANOTHER CURRENT LEADCONNECTED TO THE OTHER OF SAID CONTACT MEMBERS AT A POINT THEREONCLOSEST TO ITS INTERMEDIATE CONTACT, SAID MOVABLE CONTACT MEMBER BEINGMOVABLE RELATIVE TO SAID STATIONARY CONTACT MEMBER FROM A CLOSEDPOSITION IN WHICH AT LEAST SAID MAIN AND INTERMEDIATE CONTACTS ARE INENGAGEMENT WITH EACH OTHER, THEREBY CAUSING ELONGATED PARALLEL CURRENTBRANCHES IN SAID CONDUCTIVE PATHS OF SAID STATIONARY AND MOVABLE CONTACTMEMBERS WHICH TEND TO MAINTAIN SAID MOVABLE CONTACT MEMBER IN ITS CLOSEDPOSITION, TO AN INTERMEDIATE POSITION IN WHICH ONLY SAID ARCING CONTACTSARE IN ENGAGEMENT WITH EACH OTHER, THEREBY CAUSING ELONGATEDANTIPARALLEL CURRENT BRANCHES IN SAID CONDUCTIVE PATHS OF SAIDSTATIONARY AND MOVABLE CONTACT MEMBERS WHICH TEND TO MOVE SAID MOVABLECONTACT MEMBER OUT OF ITS INTERMEDIATE POSITION TOWARD ITS OPEN POSITIONIN WHICH NONE OF SAID CONTACTS IS IN ENGAGEMENT WITH ANY ANOTHER.